The present invention relates generally to heat exchangers, and more particularly to finned tube heat exchanger coils having sine-wave like plate fins including delta wing and ramp wing enhancements for generating counter rotating vortices for both bulk fluid mixing and boundary layer scrubbing.
Plate fins utilized in the air conditioning and refrigeration industry are normally manufactured by progressively stamping a coil of flat plate fin stock and then cutting the stamped fin to the desired length. The fins are then collected in the proper orientation and number in preparation for forming a coil. Previously formed hairpin tubes are then inserted through openings within the fins and thereafter expanded to form mechanical and thermal connections between the tubes and fins. The open ends of the hairpin tubes are fluidly connected by way of U-shaped return bends, and subsequently the return bends are soldered or brazed in place.
The plate fins are typically manufactured in a plurality of dies to form the fin shape, as well as surface enhancements on the fin, and openings through which hair pin or straight tubular members are inserted.
Generally, the HVAC industry presently forms a plurality of rows of fins simultaneously from a single roll of flat plate fin stock. These multi-row fins are cut to the desired number of rows for the coils and are then collected on stacking rods or within a box or some other means to form a pile or stack of fins ready to be laced with hairpin tubes or the like to form the coil.
It is known that a fundamental contributor to the limiting of local convective heat transfer is the establishment and persistence of a thick hydrodynamic boundary layer on the plate fin surfaces of heat exchangers. For this reason, prior art fins are provided with a variety of surface variations or enhancements, for example, lances or louvers, to restart or disrupt the boundary layer and, thus increase the transfer of heat energy between the fluid passing through the tubular members and the fluid passing over the plate fin surfaces. These prior art enhanced fins are generally either enhanced flat fins or convoluted fins. Flat fins are generally enhanced by manufacturing raised lances therein. A raised lance is defined as an elongated portion of fin formed by two parallel slits whereby the stock between the parallel slits is raised from the surface of the fin stock. In addition to having raised lances, enhanced fins may also have louvered enhancements. A louver is defined as a section of fin stock having one or two elongated slits wherein the portion of fin stock moved from the surface of the fin stock always has at least one point remaining on the surface of the fin stock. These lances and louvers promote restarting or thinning of the hydrodynamic boundary layer, thus increasing the local heat transfer coefficient. However, generally large numbers of lances and louvers are added to a surface to improve the heat transfer. These enhancements are always accompanied by an increase in pressure drop through the coil. Further, such lanced and louvered plate fins may be difficult and costly to manufacture.
Thus, there is a clear need for a sine-wave like plate fin having a combination of alternating delta wing and ramp wing enhanced surface which results in a more favorable balance of heat transfer enhancement to fluid pressure loss by providing both bulk core fluid mixing and direct boundary layer scrubbing or mixing.